In vitro maturation and in vitro fertilization oocyte (in vitro-produced embryo) has been used recently for the purpose of breeding and growing superior species in mammals. Additionally, the technique for in vitro producing embryo has also been utilized for the production of transgenic animals or clone animals.
In vitro-produced embryo can be generated for porcine [Theriogenology, Vol. 31, p. 1201–1207, 1989], but the resulting blastocyst is poor in quality, with the total cell number of about 35, which is extremely less compared with that of the in vivo-derived blastocyst at the same stage (total cell number of about 60 to 165).
First success has been attained in the production of piglet, more recently, by transferring a blastocyst to a female pig recipient [Theriogenology, Vol. 53, p. 361, 2000]. However, the number of piglets produced is only one to two, inefficiently. The reason why the technique cannot make a progress may possibly reside in the immaturity of the technique for the in vitro culture of in vitro-produced embryo.
According to the last report by some of the present inventors [Biology of Reproduction, Vol. 60, p. 336–340, 1999], it was verified that the in vitro culture of in vitro-produced embryo for a term as short as one or two days deteriorated the development ratio into fetus and infant after transfer.
For culturing in vitro-produced porcine embryo, the NCSU culture medium [Journal of Reproduction and Fertility Supplement, Vol. 48, p. 61–73, 1993] has been used widely. The culture medium contains glucose as an energy source. Glucose is a great energy source, but a possibility is suggested that the metabolites in the form of peroxide might potentially affect the culturing cell adversely. In embryo, in particular, the metabolites cause a concern of adverse effects on the gene expression and the cell cycle progress.
In such circumstances, it is desired to improve the in vitro culture technique of in vitro-produced porcine embryo.